title: Cationic uremic toxins affect human renal proximal tubule cell functioning through interaction with the organic cation transporter.
abstract: Several organic cations, such as guanidino compounds and polyamines, have been found to accumulate in plasma of patients with kidney failure due to inadequate renal clearance. Here, we studied the interaction of cationic uremic toxins with renal organic cation transport in a conditionally immortalized human proximal tubule epithelial cell line (ciPTEC). Transporter activity was measured and validated in cell suspensions by studying uptake of the fluorescent substrate 4-(4-(dimethylamino)styryl)-N-methylpyridinium-iodide (ASP(+)). Subsequently, the inhibitory potencies of the cationic uremic toxins, cadaverine, putrescine, spermine and spermidine (polyamines), acrolein (polyamine breakdown product), guanidine, and methylguanidine (guanidino compounds) were determined. Concentration-dependent inhibition of ASP(+) uptake by TPA, cimetidine, quinidine, and metformin confirmed functional endogenous organic cation transporter 2 (OCT2) expression in ciPTEC. All uremic toxins tested inhibited ASP(+) uptake, of which acrolein required the lowest concentration to provoke a half-maximal inhibition (IC50 = 44 ± 2 μM). A Dixon plot was constructed for acrolein using three independent inhibition curves with 10, 20, or 30 μM ASP(+), which demonstrated competitive or mixed type of interaction (K i = 93 ± 16 μM). Exposing the cells to a mixture of cationic uremic toxins resulted in a more potent and biphasic inhibitory response curve, indicating complex interactions between the toxins and ASP(+) uptake. In conclusion, ciPTEC proves a suitable model to study cationic xenobiotic interactions. Inhibition of cellular uptake transport was demonstrated for several uremic toxins, which might indicate a possible role in kidney disease progression during uremia.
authors.affiliation: Department of Pediatric Nephrology, Radboud University Nijmegen Medical Centre, 6525 GA, Nijmegen, The Netherlands.
authors.forename: Carolien M S
authors.initials: CM
authors.lastname: Schophuizen
authors.forename: Martijn J
authors.initials: MJ
authors.lastname: Wilmer
authors.forename: Jitske
authors.initials: J
authors.lastname: Jansen
authors.forename: Lena
authors.initials: L
authors.lastname: Gustavsson
authors.forename: Constanze
authors.initials: C
authors.lastname: Hilgendorf
authors.forename: Joost G J
authors.initials: JG
authors.lastname: Hoenderop
authors.forename: Lambert P
authors.initials: LP
authors.lastname: van den Heuvel
authors.forename: Rosalinde
authors.initials: R
authors.lastname: Masereeuw
mesh_terms: D000171:Acrolein / Q000494:pharmacology*; D015317:Biogenic Polyamines / Q000494:pharmacology*; D002412:Cations / Q000378:metabolism*; D002460:Cell Line; D006146:Guanidines / Q000494:pharmacology; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D027701:Organic Cation Transport Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D000075102:Organic Cation Transporter 2; D011726:Pyridinium Compounds; D014118:Toxins, Biological / Q000494:pharmacology*; D014511:Uremia / Q000503:physiopathology*
chemical_list: C032315:4-(4-dimethylaminostyryl)-1-methylpyridinium; D015317:Biogenic Polyamines; D002412:Cations; D006146:Guanidines; D027701:Organic Cation Transport Proteins; D000075102:Organic Cation Transporter 2; D011726:Pyridinium Compounds; C491013:SLC22A2 protein, human; D014118:Toxins, Biological; C026865:uremia middle molecule toxins; D000171:Acrolein